As environmentally friendly vehicles, vehicles such as electric vehicles and hybrid vehicles are drawing significant attention. Each of such vehicles includes: a motor for generating driving power for traveling; and a rechargeable power storage device storing electric power to be supplied to the motor. It should be noted that the hybrid vehicles include: a vehicle including an internal combustion engine in addition to the motor as a motive power source; a vehicle including a fuel cell in addition to the power storage device as a direct-current power source for driving the vehicle; and the like.
As with the electric vehicles, there has been also known a hybrid vehicle chargeable from an external power source to the power storage device of the vehicle. For example, a so-called “plug-in hybrid vehicle” has been known which is adapted such that its power storage device can be charged from a power source in a general house by connecting a power receptacle of the house to a charging inlet of the vehicle via a charging cable.
Meanwhile, wireless power transmission has been drawing attention recently as a method for transmitting electric power. The wireless power transmission does not employ a power cord or a power transmission cable. The following three known wireless power transmission techniques are promising: power transmission employing electromagnetic induction; power transmission employing electromagnetic wave; and power transmission employing a resonance method.
Among these, the resonance method is a contactless power transmission technique in which a pair of resonators (for example, a pair of resonant coils) are resonated with each other in an electromagnetic field (near field) to transmit electric power via the electromagnetic field. With the resonance method, a large electric power of several kW can be transmitted in a relatively long distance (for example, several meters). Because the large electric power is generated in the resonant coils in the resonance method, a demand arises in detecting a malfunction of such resonant coils in order to prevent failure of the system due to heat generation or the like.
Japanese Patent Laying-Open No. 11-164497 (PTL 1) discloses a technique of stopping supply of electric power to a circuit in response to a malfunction, which is identified when a pickup coil's temperature detected by a temperature sensor exceeds a certain value in a contactless power supply device that employs electromagnetic induction.